Multi-layer heat insulating material



May 22, 1956 T. M. ELFVING MULTI-LAYER HEAT INSULATING MATERIAL FiledNov. 4, 1952 IN VEN TOR.

T110192 M Eur/ma. B Y

MULTI-LAYER HEAT INSULATING MATERIAL Thore M. Elfving, San Mateo,Calif., assignor to lsoflex Corporation, Redwood City, Calif.

Application November 4, 1952, Serial No. 318,628

6 Claims. (Cl. 154-45) My present invention relates to heat insulatingboard of the multi-layer type and more particularly to an improved heatinsulation comprising a plurality of aluminum foils of hard and brightfinish laminated in a board with a light Weight pervious spacing elementwhich can be easily handled and used in complicated structures such asrefrigerated railway cars and trucks, aeroplanes and the like.

The principal object of my invention is to provide an insulating boardof light weight suitable for the use in the low temperature field andespecially in the refrigeration transportation field where moisturemigration by diffusion from the warm side of the refrigerated structureoften causes serious trouble.

A further object of the invention is to provide a light weightinsulation board of multi-layer aluminum foil in which direct metalconductivity is prevented by interspaced low conductive material.

Another object of the invention is to provide a light weight heatinsulation board-like structure in which heat radiation is effectivelyrestricted by a plurality of double acting aluminum foils and in whichconvection fiow is restricted by a large number of layers and moisturemigration by diffusion in a transversal direction is practicallyprevented by impervious metallic vapor barriers.

In the operation of air conditioned or refrigerated railway cars ortrucks considerable difiiculty is experienced in eliminating condensedwater within the insulation space or water entering the insulation fromthe commodity space. Unless proper drainage is provided, moisture willaccumulate and reduce the efficiency of the insulation. At lowtemperatures even ice can be formed within the insulating material witha detrimental increase of the heat transfer as a result. It is thereforea further object of the invention to provide a light weight insulationboard with self draining properties so that Water entering within itsstructure can not seriously affect its insulation properties.

Other objects and advantages of the invention will be in part evident tothose skilled in the art and in part pointed out herein often inconnection with the accompanying drawing wherein there is shown by wayof illustration and not of limitation several preferred embodimentsthereof.

In the drawing:

Figure l is a fragmentary perspective view of a heat insulation boardconstructed in accordance with my invention,

Figure 2 is a fragmentary perspective view showing a modification of theheat insulation board, and

Figure 3 is a fragmentary perspective view showing another modificationof the heat insulating board.

In Figures 2 and 3 of the drawing, the aluminum foils are shown asseparated by a low conductivity material, but it is to be understoodthat an insulating board made in accordance with the invention, maycomprise any number of foils and intervening layers of low conductivenited States Patent O 2 material depending upon the desired thickness ofthe board.

For a more detailed description of the invention reference is now had toFigure lot the accompanying drawing where the numerals 11 and 13designate two bright and hard corrugated aluminum foils which, accordingto the invention, may vary from .0003 to .003 inch in thickness. Thesealuminum foils are separated by a similarly corrugated plastic film 12,the corrugations extending substantially between two parallel imaginarysurfaces. The film may be of cellulose acetate, poly vinyl chloride orsilicone plastic; This plastic film material like the aluminum foil isquite thin and may vary from .001 to .003 inch in thickness. 1

The upper crests or ridges of the three corrugated foils as shown arerespectively designated by the numerals 14, 16 and 18, and the lowerridges are designated by the numerals 15, 17 and 19 respectively, theopposite sides of the ridges being considered as valleys. At the pointswhere the ridges cross and contact each other the corrugated sheets aresecured together in any conventional or convenient way as with asuitable cement or glue.

The gluing of the corrugated foils offers particular difficultiesbecause of the different nature of contacting surfaces. The metal foilshave to be glued to a nonmetallic or plastic film material with awaterproof and strong bond. According to the invention, this gluing canbe executed by using a copolymer consisting of 87% vinyl chloride, 12%vinyl acetate and 1% maleic acid. To one part of copolymer is added fiveparts of isopropyl acetate or normal propyl acetate but other solventsmay also be used. The presence of maleic acid causes an attack on themetal foils and results in a bond between the plastic and the metal thatwill not be affected by water.

The corrugation or valley depth of the aluminum foils may, according tomy invention, vary from A; to of i an inch and the corrugations of theplastic film may vary from a minimum of /s of an inch inch in depth.

The plastic film material should preferably be of a non-inflammablecharacter, as indicated by the materials mentioned above. In the use ofa cellulose acetate film material, the plasticizing agent, if such amaterial is used, should be triphenyl phosphate and/or, tri-cresylphosphate in order to render the material non-inflammable to thegreatest possible degree.

When the thicknesses of the plastic film materials are between .001 to.003 inch, as set forth above, they will be pervious to long wave heatrays. For this reason an 2.1- plastic insulation board of corrugatedfilm material having said thickness cannot be successfully used withoutincorporating in the plastic material a finely divided blockingsubstance such as graphite, usually in the amount of 35% by weight.

With an insulation board constructed according to this invention, nosuch blocking agent for the heat rays is required in the film materialeven though the plastic film between two layers of corrugated aluminumfoils is pervious to heat rays. it is a special feature of thisinvention that the interspaced low conductive non-metallic materialbetween the reflective layers of metallic foil allows heat radiation topass through without being wholly absorbed. The penetration of heat raysin the range corresponding to temperatures from 40 F. to F. varies forthe plastic materials mentioned above from 5 to 50% according to theparticular material and thickness of the film used and the heat wavelength.

As an example of an application of the invention, with a celluloseacetate film material, having a thickness of .00135 inch and corrugatedto aheight of inch, the heat ray penetration through such a film is lessthan 10% to a maximum of one for heat rays in the above mentioned rangeof temperature. it has been demonstrated by numerous tests that aninsulation board using clear transparent plastic film of the above typeand dimensions as a spacing material between aluminum foils corrugatedto a height of A" gives an sulation board with an approximately 25%lower k-factor than a board of exactly the same structure of aluminumfoils and plastic film in which the film material has been madeimpervious to heat rays by the incorporation of approximately 3% offinely dispersed graphite in the film material. The reason for thissuperiority of the clear pervious material as a spacer between thereflective metal foils is believed to be partly explained by the lowerheat conductivity of the film material. In other words, theincorporation of graphite in the plastic film increases the conductionof heat in the material considerably and thereby also increases the heattransmission through the whole insulation board. The problem of heattransfer through multilayer insulation board according to the inventionis, however, extremely complex. It involves not only an exchange ofradiation between adjacent layers of different foil and film material,but also in case the film material is pervious to heat rays, an exchangeof radiation between the reflective foils themselves through theinterspacing pervious material and the influence of the perviousness ofthe spacing material. Repeated tests, however, have shown that theincorporation of blocking material in the film leads to an inferiorproduct.

Reference is now made to Figure 2 of the drawing where there is shownanother embodiment of the invention. In this showing the board isillustrated as of two corrugated aluminum foils 2t and 21, separated byan interposed blanket 22 of fiber glass or similar material, the blankethaving yielding fibrous surfaces and, although fibrous, it is ofapproximately uniform thickness throughout. The number of alternatelayers of foil and fiber glass of which the board may be constructed isimmaterial.

In this instance, the corrugated metallic aluminum foils are cemented orglued to the non-metallic, pervious spacing material in any conventionalor convenient way along the ridges 23 and 24. This leaves theintervening valleys formed by the corrugations of the aluminum foilsubstantially free of the spacing material. The glue material alreadydescribed above will be found suitable.v The range of thickness'of thealuminum foil is the same as mentioned above with the arrangement ofFigure l and a suitable thickness of hard and bright aluminum foil isapproximately .00065 of an inch. The corrugation height of the aluminumfoils may in this modification of the invention vary from A2 of an inchto /4 of an inch.

The fiber glass spacing material 22 should have a thickness not lessthan Mr inch and should not exceed 1 inch. The fiber glass blanket 22should also be light in weight and have a weight per unit volume of notless than .5

lb./cu. ft. and not exceeding 5 lbQ/cu; ft. Such materials arepenetrated by long wave heat rays to a considerable depth varying from 1inch to over 4 inches depending upon compactness and weight of thematerial. The fiber glass spacing material used in a heat insulatingboard, according to the invention is therefore to a great extent alsopervious to heat rays. The incorporation of a blocking material withinthe fiber glass increases the k-factor of the multi-layer insulationboard and this perviousness of the spacing material is therefore one ofthe characteristics of my invention.

In this particular embodiment of the invention it will In Figure 3 ofthe drawing 1 have shown an arrangement wherein the metallic foils and21 are alternately disposed between a plurality of the fiber glassblankets 22 with the corrugations of the foils 20 and 21 extending atright angles to each other. By this particular structure I provide asubstantially uniform stiffness for the unit in directions at rightangles to each other. In these latter embodiments, the fiber glassspacing members or blankets 22 are of a softness of texture or densityof mass which will yieldingly support the aluminum foils in spacerelation under all conditions of handling and operation undulysubjecting the corrugations of the foils to distortion due to shocks orjars. In other words, the fiber glass foil spacing means or blanket 22has a softness or resiliency of texture of a sufficiently light mass sothat it will yield and then spring back in order to absorb pressuresapplied normally to the insulating board. I

An insulation board of this type is completely noncombustible and has ak-factor which is lower than that of an all-fiber glass insulation.Moisture migration by diffusion of water vapor in the transversedirection is practically inhibited by the numerous layers of metal foilsand internal convection and radiation of heat is for the same reasonminimized.

Whereas self drainage is practically complete in the first describedboard consisting of interspaced plastic film material because of theabsence of capillarities. the drainbe noted, as shown in Figure 2 of thedrawing, that the corrugations of the several superimposed aluminumfoils may be disposed parallel with each other as in the case of thefirst described embodiment. The folds of the corrugations shouldpreferably be sharp and by closely spacing these corrugationsirrespective of varying depths it is possible greatly to increase thecompressive strength ofthe several foils without materially reducing theheat insulating characteristic thereof.

age of the latter described modifications, utilizing fiber glass blanketmaterial as spacing material, is superior to fiber glass alone as thewhole insulation space never can be completely soaked with water. Thespaces defined by the corrugations in the aluminum foils are notoccupied by fiber glass and therefore constitute air layers which willalways maintain a high insulation ethciency and also form drainagechannels that will carry away and prevent the accumulation of moisture.

The light weight heat insulation board of the character described has anextremely low k-factor when in a dry condition. The factor iscomparatively little affected by a rise in the mean temperatures of theinsulation and is less influenced by moisture migration than are otherhitherto known light weight insulation boards. An insulating board,constructed in the manner described, is also resilient, as to the fiberglass portion'while remaining relatively stiff as to the foil portionand is easy to handle and cut and can therefore be applied incomplicated structures.

While my present invention may find many and varied uses it is for thepurposes of this application described as primarily designed for use inthe refrigeration transporf tation field where a minimum of weightcombined with the qualities pointed out above are of paramountimportance.

While I have, for the sake of clearness and in order to disclose theinvention so that the same can be readily understood, described andillustrated several specific forms and arrangements, it is to beunderstood that the invention is not limited to the specific formsdescribed, but may be embodied in other forms that will suggestthemselves topersons skilled in the art. It is believed that thisinvention is new and it is desired to claim it so that all such changesas come within the scope of the appended claims are to be considered aspart of this invention.

Having thus described my invention, what I claim and .desire to secureby Letters Patent is:

1. In a multi-layer heat insulating board, the combina- ;-tion of aplurality of spaced impervious sheets of reflective metal foil eachhaving corrugations extending paral- ,lel to each other, said sheetsforming vapor, convection and radiation barriers, and a blanket ofinsulating material of substantial thickness disposed between saidsheets and secured directly-to the apexesof the corrugatio ns andserving to provide insulation between foils, said corrugations beingopen and unobstructed whereby to provide drainage channels between thefoil and the insulating material.

2. A multi-layer heat insulating board as in claim 1 wherein saidblanket of insulating material is formed of a glass fiber blanket.

3. A multi-layer heat insulating board as in claim 1 wherein said glassfiber blanket is of a density of from .5 lb. to 5.0 lbs. per cubic footso that it is pervious to long wave heat rays.

4. In a multi-layer heat insulating board, the combination of aplurality of spaced impervious sheets of reflective metal foil eachhaving corrugations extending parallel to each other, said sheetsforming vapor, convection and radiation barriers, and a plurality ofblankets of insulating material of substantial thickness disposedbetween said foils and secured directly to the apexes thereof andserving to provide insulation between the foils, said corrugations beingopen and unobstructed whereby to provide drainage channels for moisturecondensed thereon.

5. A multi-layer heat insulating board as in claim 4 wherein saidblanket of insulating material is formed of a glass fiber blanket.

6. A multi-layer heat insulating board as in claim 4 wherein said glassfiber blanket is of a density of from .5 lb. to 5.0 lbs. per cubic footso that it is pervious to long wave heat rays.

References Cited in the file of this patent UNITED STATES PATENTS1,020,567 MOeller Mar. 19, 1912 2,029,679 Seving et al. Feb. 4, 19362,037,813 Munters Apr. 21, 1936 2,206,059 Slayter July 2, 1940 2,221,309Gazelle Nov. 12, 1940 2,329,456 Campbell Sept. 14, 1943 2,330,941 AcuifOct. 5, 1943 2,406,815 Elfving Sept. 3, 1946 2,514,170 Walter et al.July 4, 1950 FOREIGN PATENTS 448,543 Great Britain June 10, 1936 459,574Great Britain June 17, 1936 482,809 Great Britain Apr. 5, 1938

1. IN A MULTI-LAYER HEAT INSULATING BOARD, THE COMBINATION OF APLURALITY OF SPACRD IMPERVIOUS SHEETS OF REFLECTIVE METAL FOIL EACHHAVING CORRUGATIONS EXTENDING PARALLEL TO EACH OTHER, SAID SHEETSFORMING VAPOR, CONVECTION AND RADIATION BARRIERS, AND A BLANKET OFINSULATING MATERIAL OF SUBSTANTIAL THICKNESS DISPOSED BETWEEN SAIDSHEETS AND SECURED DIRECTLY TO THE APEXES OF THE CORRUGATIONS ANDSERVING TO PROVIDE INSULATION BETWEEN FOILS, SAID CORRUGATIONS BEINGOPEN AND UNOBSTRUCTED WHEREBY TO PROVIDE DRAINAGE CHANNELS BETWEEN THEFOIL AND THE INSULATING MATERIAL.